By Jan Carabeo

PHILADELPHIA (CBS) – McClure Elementary School is closed Friday for additional cleaning. School district officials say two air samples for asbestos came back slightly elevated after testing was done on Thursday night.

Frustration is growing at the school in Hunting Park. Parents and teachers say they are tired of wondering if their health is at risk and if the school district is taking their concerns seriously.

“I feel disgusted. No one cares about the children,” teacher Lisa Handy said.

She says the latest contamination was discovered near her fourth-grade classroom.

“They closed school today. They said there would be a massive cleaning. And we can’t trust that,” she said.

“McClure will remain closed today for additional cleaning and further testing to ensure student and staff safety,” the School District of Philadelphia said in a statement.

“Indeed, overnight test results that came back this morning yielded elevated levels of asbestos, indicating that our concerns and outrage were absolutely warranted,” Philadelphia Federation of Teachers President Jerry Jordan said. “Our recommendations are borne out of decades of experience. Our Director of Environmental Science has been one of the preeminent experts in his field for decades. Our recommendations yesterday were not made out of an overabundance of caution. They were made based on science.”

This comes as members of the Philadelphia teachers’ union held a rally Friday morning at McClure Elementary School. They say the school is unsafe after recent testing showed “alarming” levels of asbestos.

A union scientist who conducted the testing on Tuesday says the district failed to seal a contaminated attic, leading to elevated asbestos levels in the air.

The union plans to file a lawsuit.

Students and staff returned to school on Monday for the first time in three weeks because of the toxic material.

Parents now wonder if that was the right decision.

“From the beginning, we said keep the doors closed until all the work is done. You hear about mesothelioma. I don’t want that later on in life for my children,” Chenoa Manley said.

The union has been critical of the school district’s handling of asbestos issues.

On Thursday, the union said the district failed to properly seas a “contaminated attic” leading to elevated asbestos levels at McClure on Tuesday as well.

“We want transparency. We want the district to stop lying and saying the buildings are safe,” Rachel Boschen said.

The school district says it follows industry best practices and will continue to collaborate with the teachers’ union on testing protocols.

You can read the full statement issued by the teachers’ union here.

To see the results from the testing, click here.